What is the principal characteristic of a tunnel diode?

The principal characteristic of a tunnel diode is its negative resistance region. This phenomenon occurs due to quantum mechanical effects, specifically tunneling, which allows electrons to pass through the potential barrier at certain voltage levels. In a tunnel diode, as the voltage increases, the current initially increases until a certain point where further increases in voltage lead to a decrease in current—this is the negative resistance area.

This property is highly useful in various applications, particularly in high-frequency oscillators and amplifiers, as the unusual current-voltage relationship enables the device to operate effectively in these ranges. Tunnel diodes are also known for their fast operation due to their low junction capacitance, but the defining feature that sets them apart from other diodes is the presence of that negative resistance region in their I-V characteristic curve.